Lutein, one of xanthophylls in the family of carotenoids with non-pro-vitamin A activity, is a fat-soluble yellowish pigment found mostly in higher order of plants, algae and photosynthetic bacteria. Lutein and other carotenoids cannot be biosynthesized by animals or insects. Their presence in animals is attributed to ingestion via food and accumulation in certain tissues. Lutein and its isomer, zeaxanthin, have been identified as the only carotenoids present in specific eye tissues, specifically the macular fovea, a small area of the retina responsible for central vision and high visual acuity. In humans and in plants, lutein is believed to function as a filter of high energy blue light and is an antioxidant that quenches and scavenges photo induced reactive oxygen species (ROS) which are highly reactive and can damage DNA and lipids. Studies have shown that sufficient daily intake of lutein can greatly lead towards reducing the risk of eye diseases such as aged-related macular degradation (AMD), the leading cause of blindness among the elderly, and cataracts. Besides its bioavailability as potent antioxidant, recent studies suggest that xanthophylls, especially lutein, can be directly link to prevention of certain-types of cancer. Presence of lutein in skin and oral consumption may also serve to protect skin from UV-induced damage and may reduce the risk of cardiovascular.
Although lutein can be found in human diets with most abundantly in dark, leafy green such as spinach and kale, and foods with yellow color, such as corn and egg yolk, the average daily intake of lutein is insufficient to reduce the risk of eye diseases as well as other related symptoms. Moreover, humans can carry out only limited metabolic transformations of carotenoids, suggesting that the sufficient consumption of specific dietary carotenoids be certainly needed.
Yellow silk cocoon is one of some cocoons from many varieties of the silkworm, Bombyx. mori. The pigments in yellow or golden-yellow cocoons are derived from carotenoids, whereas the cocoons in others color such as yellowish green and green sasa are from flavonoids. These pigments are absorbed from mulberry leaves. They are then transferred from a midgut to silk gland via the hemolymp, and eventually accumulated in the layers of the cocoon sericin. It is emphasized that among these carotenoids, xanthophylls, principally lutein, have been indicated in previous study as predominant carotenoids in the yellow cocoons. For silk textiles, pigments partially removed from the silk cocoons do not go on to be used for other applications. Moreover, silk protein like sericin, the second main constituent of silk fibers at 20-30% of the total cocoon weight, is also mostly removed from the cocoon during degumming process. Wastewater from such process contains both lutein and sericin and is hardly treated by common wastewater management system. However, the unique functional properties of both lutein and sericin be used in food and cosmetic products as valuable natural ingredients. Consequently, isolation and extraction as well as characterization of silkworm, B. mori, in a form of lutein-binding protein, have been investigated.
Xanthophylls and carotene are lipid-soluble molecules that follow the absorption pathway of dietary fat. The absorption involves several steps starting from breakdown of food matrix to release of carotenoids into the lumen of the gastrointestinal tract through their incorporation into lymphatic lipoproteins. The efficient digestion and absorption of dietary fat, as well as the presence of bile salt micelles, is essential for carotenoid absorption. The study of competition among carotenoids and other dietary components for absorption, transport, and uptake by tissues well documented but requires further research. From limited data, it seems that the more polar carotenoids, xanthophylls, may be absorbed more efficiently than are carotenes, hydrocarbon carotenoids. Therefore, xanthophylls, particularly lutein and its metabolic products are well solubilized and are incorporated into surface of lipoproteins such as chylomicrons, LDL and HDL. These may enhance the transportation of lutein via blood circulating system and then accumulated in specific tissues, whereas 80-85% of hydrocarbon carotenoids preferably accumulate in the adipose tissues. In human serum, only six major carotenoids, particularly lutein and lycopene, have an estimated half life for 11-14 days. Take up of carotenoids differ for different tissues with lutein and zeaxanthin specifically accumulating in the macula region of the eye and strong associating with the decrease of AMD risk.
Lutein from Marigold flowers is an important source of lutein available in the market. It is composed of 94-97% lutein esters and 3-6% zeaxanthin. After consumption, the lutein esters need to be acid hydrolyzed into free lutein in the stomach before being absorbed into the blood serum. As several studies have indicated, only specific form of lutein can get into the blood serum and accumulate in certain organ tissues, especially the macula fovea. Lutein in the form that can be readily absorbed into the blood stream has higher bioactivity and bioavailability. Acid condition has been found to have an effect on lutein isomer transformation from E to Z form. Moreover, only lutein binding protein is found in the macula fovea, whereas lutein esters are dectected in skin and fat tissues.
Typical methods exist for isolating and purifying lutein from different plants such as marigold flowers, marigold meal, algae, red peppers, and other plant materials. Lutein isolated from these materials is in the form of an ester. The isolation processes used are complicated and involved with halogenated organic solvents. Additionally, plants and flowers used may contain a high level of herbicide and pesticide residue.
U.S. Pat. No. 5,382,714 describes a process for isolation, purification, and recrystallization of lutein from saponified marigold oleoresin. The starting material, saponified marigold oleoresin, also known as kemin yellow oil, is available commercially. After lutein isolation, the concentration of lutein crystal is around 70%. The lutein crystal is recrystallized in a mixture of dichloromethane and hexane to achieve a lutein purity level of more than 97%. The use of halogenated organic compounds in food industry is under strict regulation many territories.
PCT patent application no. WO03037833 A1 describes a method for extraction lutein from marigold meal using supercritical fluid extraction.
U.S. Pat. No. 7,173,145 B2 describes a process for extracting and purifying lutein, zeaxanthin, and rare carotenoids from marigold flowers and plants. Use of a mixture containing tetrahydrofuran and methanol was disclosed. The disadvantages of this method are the creation of a high caustic condition and the toxicity of methanol during extraction.